ok in the trailer for halo 4, the master chief wakes up to the frigate exploding. he gets cortana and uses his jet pack to get out there ( woah hold up, when did chief have a jetpacK) he flies through the ship and reachs the hull and then it shows he is facing a massive structure which is weird because at the end of halo 3 it showed a large planet, instead it shows a forrunner structure